1. Technical Field
The present invention relates to a liquid ejecting head inspection apparatus for inspecting the discharging of liquid droplets from a liquid ejecting head, which is a head that can eject liquid. In addition, the invention relates to a liquid ejecting apparatus and an inspection method of a liquid ejecting head inspection apparatus.
2. Related Art
An ink-jet recording apparatus such as an ink-jet printer, a plotter, or the like is provided with an ink-jet recording head. The ink-jet recording head discharges ink retained in an ink container such as an ink cartridge, an ink tank, or the like in the form of ink droplets.
An ink-jet recording head has a plurality of pressure generation chambers each of which is in communication with the corresponding one of a plurality of nozzle holes, a reservoir (manifold) that is in communication with the plurality of pressure generation chambers and functions as a common liquid chamber, and a plurality of pressure generation elements (pressure generating means) each of which generates a pressure change inside the corresponding pressure generation chamber to discharge a liquid droplet from the corresponding nozzle hole. Examples of the pressure generating means mounted in an ink-jet recording head are: longitudinal vibration type piezoelectric elements, deflection vibration type piezoelectric elements, electrostatic actuator devices, heating elements, or the like.
In order to guarantee predetermined print quality, an ink-jet recording apparatus that is provided with an ink-jet recording head performs missing-dot detection operation (discharging inspection/non-discharging inspection) at predetermined timing before printing. Various methods for missing-dot detection have been proposed. For example, the following missing-dot detection method has been proposed in the art. A voltage is applied between a nozzle plate (nozzle holes) and an inspection region that includes a liquid absorber so as to charge ink electrically. The electrically charged ink is ejected. A potential signal that represents a change in potential (i.e., voltage level) between the inspection area and the nozzle plate is outputted as a result of the discharging (i.e., ejecting) of the electrically charged ink. On the basis of the amplitude of the potential signal, missing dot detection can be performed. The above missing-dot detection method is disclosed in JP-A-2007-38566. The proposed missing-dot detection method utilizes a difference between the amplitude of a potential signal outputted when the charged ink is properly discharged and the amplitude of a potential signal outputted when the charged ink is not properly discharged.
A change in a potential signal (amplitude) obtained from an ink droplet is very small. For this reason, it is necessary to amplify a change in a potential signal in order to successfully detect the change in the potential signal attributable to the charged ink droplet. Because of the effects of noise on a discharging drive signal, in some cases, a change in a potential signal that is the same as that under proper ink-droplet discharging conditions, that is, conditions under which ink droplets are discharged properly, is mistakenly detected even when it should not be detected because no ink droplet is actually discharged or because ink droplets are not discharged fully. Such erroneous detection makes it impossible to conduct inspection accurately.
The problem identified above is not unique to an ink-jet recording head inspection apparatus. That is, the same problem could also arise in various kinds of liquid ejecting head inspection apparatuses.